When firing a sub-calibre projectile from a gun barrel it is previously known to use annular sabots to bridge the annular gap between the projectile and the gun barrel. A typical sabot is then intended to achieve centering of the sub-calibre projectile in the barrel as well as the necessary obturation between the outer surface of the projectile and the inner surface of the barrel so that effective expulsion and spinning of the projectile from the firearm will be achieved.
As soon as the projectile has left the barrel the sabot has served its purpose and it should be separated from the projectile without unduly affecting the flight of the projectile. A sabot is therefore usually made in such a way that it is separated from the projectile due to the centrifugal forces, or the airflow forces, or both which act upon the sabot at the exit of the projectile from the muzzle of the barrel. For example the sabot can be made of a plurality of separate segments which are held together in the gun barrel but separated from each other at the exit of the projectile from the muzzle of the barrel. By the Swedish Pat. No. 74.10607-1 it is also previously known to make the sabot with a unitary body provided with a plurality of slots extending through the sabot and aligned parallel to its longitudinal axis and an unslotted portion which withstands the expulsion forces which act upon the projectile in the barrel at firing but which is mechanically weak so that it is broken by the centrifugal, or airflow forces or both which act upon the longitudinal sabot segments at the exit of the projectile from the muzzle of the barrel.
As sub-calibre projectiles in recent years have been used more and more, for instance against armour projected targets, it has also been more important that the sabots not only should be able to withstand the strong expulsion forces in the gun barrel but also should be simple to construct and manufacture for economical reasons. This relates to live as well as practice ammunition. The sabots should also be made of a light-weight material so that as large a part as possible of the expulsion gases are used for the expulsion of the sub-calibre projectile itself and also so that the handling of the ammunition units is facilitated. These requirements of a high strength and low manufacturing costs have been difficult to combine. The strength requirements cannot be reduced, if anything the strength requirements of the ammunition units (projectile with sabot) have increased due to the increase of muzzle velocity, and spin velocity as well as a more rapid ammunition handling procedure.
A further requirement of the sabots is that they should be designed in such a way that they can be automatically rammed into the firearm. Previously known sabots have been provided with a full caliber ring at the front end and at the rear end and an intermediate portion with reduced diameter. Such sabots, however, are not suitable for automatic ramming.